Problem: Simplify to lowest terms. $\dfrac{21}{24}$
Explanation: What is the greatest common factor (GCD) of 21 and 24? $21 = 3\cdot7$ $24 = 2\cdot2\cdot2\cdot3$ $\mbox{GCD}(21, 24) = 3$ $\dfrac{21}{24} = \dfrac{7 \cdot 3}{ 8\cdot 3}$ $\hphantom{\dfrac{21}{24}} = \dfrac{7}{8} \cdot \dfrac{3}{3}$ $\hphantom{\dfrac{21}{24}} = \dfrac{7}{8} \cdot 1$ $\hphantom{\dfrac{21}{24}} = \dfrac{7}{8}$